Chrome leather scrap or waste can consist of pieces or scraps that are trimmed from tanned hides and skins or fragmented when the tanned hide is split into one or two more layers, or can also consist of shavings or dust produced when the chrome tanned leather is machine shaved to a desired thickness.
The chrome leather scrap generally contains from about 75-80% by weight of protein, along with chromium oxide, inorganic salts and fats and oils.
Attempts have been made in the past to utilize chrome leather scrap or waste. For example, chrome leather scrap has been incinerated to produce energy, and has also been used in the past to produce adhesives or glues. In addition, chrome leather scrap has been used as a fertilizer and has also been approved in amounts less than 200 ppm of chromium for animal feed rations, but there has been little commercial interest in using the chrome leather scraps as a fertilizer or as an animal feed supplement because of the questionable effect of the chromium on animal and plant life. Thus the vast proportion of chrome leather scrap has been discarded, causing a serious environmental problem.
More recently, attempts have been made to hydrolyze the chrome leather scrap and recover the chromium compounds. In this regard, U.S. Pat. No. 4,100,154 describes a hydrolyzing process using an alkaline earth metal hydroxide, such as calcium oxide or hydroxide. In the process of that patent, the chrome leather scrap is mixed with a calcium oxide metal solution and heated to a temperature of about 200.degree. F. to produce a hydrolysate which is subsequently filtered to separate the insoluble chromium compounds. The resulting filtrate is stated to have a chromium content of less than 5 ppm and the separated chromium compounds are indicated to be reusable in the tannery process.
Similarly, the article "Utilization of Leather Waste--Animal Feedstuff from Chrome Shavings: Part 1, Pilot Plant Study", Reis and Beleza, Journal of the Society of Leather Technologists and Chemists, Vol. 75, p. 15, describes an experimental process for removing chromium from chrome leather waste using calcium oxide. The article suggests that the hydrolysate, after separation of the precipitated chromium compounds, can be used as an animal feed supplement.